Directional drilling involves controlling the direction of a borehole as it is being drilled. Specifically, the goal of directional drilling is to reach a target subterranean destination, typically a potential hydrocarbon producing formation, with a drill string. In order to conduct the drilling operation, specialized downhole tools are utilized. These tools often include various sensors and other electronic components or equipment for providing desired information or data concerning the environmental conditions of the surrounding formation being drilled and for providing desired information or data and communicating instructions concerning the operational and directional parameters of the drill string within the borehole.
Various downhole tools typically include an inner member, such as a rotatable shaft, extending within an outer member, such as a housing. Further, various instruments may need to be mounted within the tool in the interface between the inner and outer members. For instance, the instrument provided in the interface may be comprised of a sensor for sensing the rotation or orientation of the inner member relative to the outer member.
Further, the instrument provided in the interface may be comprised of a coupling assembly or device for communicating or transmitting electrical signals or electricity along the tool between the inner and outer members. For instance, the electrical signals or electricity may embody data, instructions or sensed information being communicated between an uphole location and a downhole sensor or electronic component or may provide power being transmitted from an uphole power source to a downhole sensor or electronic component.
For example, it is often necessary or desirable to locate or position the downhole sensor within a non-rotating member or component of a tool along a rotary drill string in order to permit or facilitate the proper functioning or operation of the sensor. Accordingly, an electrical signal embodying data communications, sensed information, instructions and/or power may need to be transmitted between a non-rotating member of the tool housing containing the downhole sensor and a rotating member of the tool connected with a drive shaft or other section of the rotary drill string. Thus, an instrument comprised of a coupling assembly or device may be mounted within the interface between the rotating and non-rotating members of the tool. It is has been found to be particularly difficult to transmit power across the interface as compared with data transmission.
For instance, slip ring assemblies are often utilized for transferring power and data between rotating and non-rotating members, as described in U.S. Pat. No. 4,031,544 issued Jun. 21, 1977 to Lapetina, U.S. Pat. No. 5,841,734 issued Nov. 24, 1998 to Ritter et. al., U.S. Pat. No. 6,238,142 issued May 29, 2001 to Harsch and U.S. Pat. No. 6,392,561 issued May 21, 2002 to Davies et. al.
The slip ring assembly provides for electrical contact between a slip ring and contact brushes, each being mounted with one of the rotating and non-rotating members of a tool. The effectiveness of the transmission of the electrical signals by the slip ring assembly is dependent upon the alignment of the contact brushes with the slip ring. Given the mounting of these components with the rotating and non-rotating members of the tool, the effectiveness of the transmission of the electrical signals is therefore dependent upon the maintenance of the longitudinal alignment between the rotating and non-rotating members. In other words, any conditions or influences on the members causing relative longitudinal movement therebetween may adversely impact the slip ring assembly.
As an alternative to the use of a slip ring assembly, power transfer and data communication may be provided by inductive coupling of the rotating and non-rotating members of a tool. For instance, an electromagnetic coupling device may be provided in the interface between the rotating and non-rotating members of the tool, as described in U.S. Pat. No. 6,244,361 issued Jun. 12, 2001 to Comeau et. al. However, inductive coupling may not be desirable in some applications. Further, inductive coupling has not been found to be as effective as a slip ring assembly for the transmission of power, as compared to data communications. Finally, any instrument mounted within the interface between the rotating and non-rotating members of the tool may be adversely impacted by the relative longitudinal movement of those members.
In particular, with respect to downhole tools, conditions may be encountered in the borehole by the tool which tend to interfere with the longitudinal alignment between the inner and outer members of the tool. In particular, downhole conditions, including vibration, temperature changes, pressure changes and the application of tension and compression forces to the tool, may result in the longitudinal movement of one member relative to the other. For instance, the inner member may undergo an amount of expansion or contraction resulting in longitudinal movement relative to the outer member. Where an instrument is mounted within the interface between the inner and outer members, this relative longitudinal movement may result in a misalignment of the components of the instrument, adversely impacting the proper operation of the instrument. For example, where the slip ring assembly is mounted within the interface, the relative longitudinal movement of the inner and outer members of the tool may result in a misalignment of the slip ring and brush contacts, thus potentially interfering with data or power transmission therebetween.
Thus, there is a need in the industry for a device or apparatus for mounting an instrument in a tool of the type comprising an inner member and an outer member, wherein the inner and outer members are capable of an amount of relative longitudinal movement and wherein the instrument is required to be mounted in the interface between the members. More particularly, there is a need for the device or apparatus to be able to compensate for the slip or relative longitudinal movement of the inner and outer members of the tool in order to permit the proper functioning or operation of the instrument.